Consider the following statements regarding the slow start phase of the TCP congestion control algorithm. Note the  stands for the TCP congestion window and MSS denotes the Maximum Segment Size.
i. The  increases by 2 MSS on every successful acknowledgement.
ii. The  approximately doubles on every successful acknowledgment.
iii. The  increases by 1 MSS every round trip time.
iv. The  approximately doubles every round trip time.
Which one of the following is correct?